Re: [dpdk-dev] [ovs-dev] OVS-DPDK performance problem on ixgbe vector PMD

["Traynor, Kevin" <kevin.traynor@intel.com>]

> -----Original Message-----
> From: dev [mailto:dev-bounces@openvswitch.org] On Behalf Of Zoltan Kiss
> Sent: Friday, August 21, 2015 7:05 PM
> To: dev@dpdk.org; dev@openvswitch.org
> Cc: Richardson, Bruce; Ananyev, Konstantin
> Subject: [ovs-dev] OVS-DPDK performance problem on ixgbe vector PMD
> 
> Hi,
> 
> I've set up a simple packet forwarding perf test on a dual-port 10G
> 82599ES: one port receives 64 byte UDP packets, the other sends it out,
> one core used. I've used latest OVS with DPDK 2.1, and the first result
> was only 13.2 Mpps, which was a bit far from the 13.9 I've seen last
> year with the same test. The first thing I've changed was to revert back
> to the old behaviour about this issue:
> 
> http://permalink.gmane.org/gmane.comp.networking.dpdk.devel/22731
> 
> So instead of the new default I've passed 2048 + RTE_PKTMBUF_HEADROOM.
> That increased the performance to 13.5, but to figure out what's wrong
> started to play with the receive functions. First I've disabled vector
> PMD, but ixgbe_recv_pkts_bulk_alloc() was even worse, only 12.5 Mpps. So
> then I've enabled scattered RX, and with
> ixgbe_recv_pkts_lro_bulk_alloc() I could manage to get 13.98 Mpps, which
> is I guess as close as possible to the 14.2 line rate (on my HW at
> least, with one core)
> Does anyone has a good explanation about why the vector PMD performs so
> significantly worse? I would expect that on a 3.2 GHz i5-4570 one core
> should be able to reach ~14 Mpps, SG and vector PMD shouldn't make a
> difference.

I've previously turned on/off vectorisation and found that for tx it makes
a significant difference. For Rx it didn't make a much of a difference but
rx bulk allocation which gets enabled with it did improve performance.

Is there is something else also running on the current pmd core? did you
try moving it to another? Also, did you compile OVS with -O3/-Ofast, they
tend to give a performance boost.

Are you hitting 3.2 GHz for the core with the pmd? I think that is only
with turbo boost, so it may not be achievable all the time.

> I've tried to look into it with oprofile, but the results were quite
> strange: 35% of the samples were from miniflow_extract, the part where
> parse_vlan calls data_pull to jump after the MAC addresses. The oprofile
> snippet (1M samples):
> 
>    511454 19        0.0037  flow.c:511
>    511458 149       0.0292  dp-packet.h:266
>    51145f 4264      0.8357  dp-packet.h:267
>    511466 18        0.0035  dp-packet.h:268
>    51146d 43        0.0084  dp-packet.h:269
>    511474 172       0.0337  flow.c:511
>    51147a 4320      0.8467  string3.h:51
>    51147e 358763   70.3176  flow.c:99
>    511482 2        3.9e-04  string3.h:51
>    511485 3060      0.5998  string3.h:51
>    511488 1693      0.3318  string3.h:51
>    51148c 2933      0.5749  flow.c:326
>    511491 47        0.0092  flow.c:326
> 
> And the corresponding disassembled code:
> 
>    511454:       49 83 f9 0d             cmp    r9,0xd
>    511458:       c6 83 81 00 00 00 00    mov    BYTE PTR [rbx+0x81],0x0
>    51145f:       66 89 83 82 00 00 00    mov    WORD PTR [rbx+0x82],ax
>    511466:       66 89 93 84 00 00 00    mov    WORD PTR [rbx+0x84],dx
>    51146d:       66 89 8b 86 00 00 00    mov    WORD PTR [rbx+0x86],cx
>    511474:       0f 86 af 01 00 00       jbe    511629
> <miniflow_extract+0x279>
>    51147a:       48 8b 45 00             mov    rax,QWORD PTR [rbp+0x0]
>    51147e:       4c 8d 5d 0c             lea    r11,[rbp+0xc]
>    511482:       49 89 00                mov    QWORD PTR [r8],rax
>    511485:       8b 45 08                mov    eax,DWORD PTR [rbp+0x8]
>    511488:       41 89 40 08             mov    DWORD PTR [r8+0x8],eax
>    51148c:       44 0f b7 55 0c          movzx  r10d,WORD PTR [rbp+0xc]
>    511491:       66 41 81 fa 81 00       cmp    r10w,0x81
> 
> My only explanation to this so far is that I misunderstand something
> about the oprofile results.
> 
> Regards,
> 
> Zoltan
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